Usually, a touch panel is an input device attached onto a display device such as LCD (Liquid Crystal Display), PDP (Plasma Display Panel), OLED (Organic Light Emitting Diode), and AMOLED (Active Matrix Organic Light Emitting Diode) and generates a signal corresponding to a touch point when an object such as a finger or pen contacts the touch panel. The touch panel is very widely used for portable devices, industrial devices, DID (Digital Information Device) and so on.
As described before, the conventional touch panel is additionally installed on the upper surface of the completed display device and is made separately from the display device. As described above, the conventional technology of additionally installing the touch panel on the upper surface of the display device has caused an increase in the thickness of the whole display device to thus lower a product competitive power, and has lowered transmissivity due to addition of the touch panel to thus deteriorate a display quality of the display device. In addition, separately different processes of manufacturing the display device and the touch panel and a process of assembling two devices different from each other, have caused an increase of a manufacturing cost.
Meanwhile, in order to solve the above problems, there has been an attempt to have touch components in a display device. Fox example, in the case of a liquid crystal display (LCD), signal lines for detecting touch inputs are arranged and wired on a thin film transistor (TFT) substrate that is a lower substrate, and a plurality of detection electrodes that are connected to the signal lines and disposed at a distance from each other are formed. A common electrode is formed all over the whole lower surface on a collar auxiliary signal line substrate that is an upper substrate. A protrusion portion connected to the common electrode is installed to protrude downwards. In addition, when pressure is applied to the upper substrate, it is detected whether or not the protrusion portion contacts the detection electrodes, to thus detect a touch input. The touch components are installed in the display device, using the thin film transistor (TFT) substrate and a color auxiliary signal line substrate. Accordingly, the touch components can be installed without a thickness increment of the display device. Further, the display device and the touch input unit can be manufactured together with a single manufacturing process.
Meanwhile, in the case of a display device such as a conventional LCD or AMOLED, gate lines and data lines are arranged on a thin film transistor (TFT) substrate that is a lower substrate, and components such as pixels, pixel electrodes, and TFTs. Thus, in the case that touch components are installed on the lower substrate of the display device, the touch components have a very complicated structure on the lower substrate of the display device. This makes a manufacturing process complex, to thereby accompany various kinds of problems of deteriorating a yield rate greatly and declining an insulation between the components.
In addition, as components for screen display and detecting touch inputs are mounted together on the lower substrate of the display device, transmissivity of a display panel is greatly lowered. Furthermore, it also becomes factors of causing rise of a process expense and decline of a yield rate to form protrusion portions electrically connected with a common electrode over a number of areas on the lower surface of the upper substrate.
In addition, liquid crystal, organic materials, plasma gas, etc., are sealed up in a display device according to kind of the display device. Since the display device detects touch inputs using bends of the upper substrate, cracks may frequently happen on real parts of the display device, and durability of the display device becomes greatly weak. In addition, when a touch input occurs, palpitation of the screen may be caused.
In addition, since protrusion portions that are projected downwards are formed on the lower surface of the upper substrate, a manufacturing process of the upper substrate is also complicated. The display device should also maintain an exact cell gap between the protrusion portion of the upper substrate and the detection electrode of the lower electrode. For this reason, an additional process of forming a planarization layer on the lower substrate is needed. In spite of using the planarization layer, it is very difficult to keep the cell gap strictly between the protrusion portion and the detection electrode, and problems of declining a yield rate, shortening a lifetime, losing a touch signal may be induced.